Doppler-nulling and two-way timing and ranging (spatial awareness)

ABSTRACT

A system is disclosed. The system may include a receiver or transmitter node. The receiver or transmitter node may include a communications interface with an antenna element and a controller. The controller may include one or more processors and have information of own node velocity and own node orientation relative to a common reference frame. The receiver or transmitter node may be time synchronized to apply Doppler corrections to signals, the Doppler corrections associated with the receiver or transmitter node&#39;s own motions relative to the common reference frame, the Doppler corrections applied using Doppler null steering along Null directions. The receiver node is configured to determine a bearing angle based on the signals based on Doppler null steering; and to determine a range based on two-way time-of-flight based ranging signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims priority from thefollowing U.S. Patent Applications:

-   -   (a) U.S. patent application Ser. No. 17/233,107, filed Apr. 16,        2021, which is incorporated by reference in its entirety;    -   (b) P.C.T. Patent Application No. PCT/US22/24653, filed Apr. 13,        2022, which claims priority to U.S. patent application Ser. No.        17/233,107, filed Apr. 16, 2021, all of which are incorporated        by reference in its entirety;    -   (c) U.S. patent application Ser. No. 17/408,156, filed Aug. 20,        2021, which claims priority to U.S. patent application Ser. No.        17/233,107, filed Apr. 16, 2021, all of which are incorporated        by reference in its entirety;    -   (d) U.S. patent application Ser. No. 17/541,703, filed Dec. 3,        2021, which is incorporated by reference in its entirety, which        claims priority to:    -   U.S. patent application Ser. No. 17/408,156, filed Aug. 20,        2021, which is incorporated by reference in its entirety; and    -   U.S. patent application Ser. No. 17/233,107, filed Apr. 16,        2021, all of which is incorporated by reference in its entirety;    -   (e) U.S. patent application Ser. No. 17/534,061, filed Nov. 23,        2021, which is incorporated by reference in its entirety;    -   (f) U.S. Patent Application No. 63/344,445, filed May 20, 2022,        which is incorporated by reference in its entirety;    -   (g) U.S. patent application Ser. No. 17/857,920, filed Jul. 5,        2022, which is incorporated by reference in its entirety;    -   (h) U.S. Patent Application No. 63/400,138, filed Aug. 23, 2022,        which is incorporated by reference in its entirety;    -   (i) U.S. patent application Ser. No. 17/940,898, filed Sep. 8,        2022, which is incorporated by reference in its entirety;    -   (j) U.S. patent application Ser. No. 17/941,907, filed Sep. 9,        2022, which is incorporated by reference in its entirety;    -   (k) U.S. patent application Ser. No. 17/957,881, filed Sep. 30,        2022, which is incorporated by reference in its entirety;    -   (l) U.S. patent application Ser. No. 17/990,491, filed Nov. 18,        2022, which is incorporated by reference in its entirety;    -   (m) U.S. patent application Ser. No. 18/130,285, filed Apr. 3,        2023, which is incorporated by reference in its entirety; and    -   (n) U.S. patent application Ser. No. 18/134,950, filed Apr. 14,        2023, which is incorporated by reference in its entirety.

BACKGROUND

Identification Friend or Foe (IFF) systems, Traffic Collision AvoidanceSystems (TCAS), and Terminal Airspace Control (TASC) systems may havecommon elements. Each of these are important in managing controlledairspaces.

IFF allows military aircraft to identify if nearby aircraft represent athreat. IFF is typically a radar-based identification system usedprimarily by military and civilian air traffic control (ATC) todistinguish between friendly, hostile, or neutral aircraft and vehicles.The primary purpose of IFF is to prevent accidental engagements orfriendly fire incidents by allowing military personnel to quickly andaccurately identify friendly forces. IFF enabled systems may beconfigured to be an interrogator. The interrogator is typically found onthe ground or on other aircraft. The interrogator is a device configuredto send out interrogation signals to query the transponders of nearbyplatforms. Once an IFF-enabled system receives the encoded response froma transmitting node, it processes this information to determine theidentity and other relevant attributes of the transmitting node.

TCAS is an avionic system designed to reduce the risk of mid-aircollisions between aircraft. TCAS uses onboard equipment to monitor theairspace around an aircraft, detect other aircraft equipped withtransponders (which transmit their position, altitude, and otherrelevant information), and provide pilots with visual and audible alertsor resolution advisories (RAs) to help maintain a safe separationbetween aircraft. TCAS tracks nearby aircraft and if notifies the pilot(or autopilot) if an evasive maneuver is required to avoid an air-to-aircollision. TASC systems such as AN/TPX-42 allow military air trafficcontrollers to track the identities and positions of aircraft operatingin a controlled airspace.

Conventionally, airspace management systems such as IFF, TCAS, and TASCsystems may be dependent to a large extent on being able to exchangeinformation (e.g., via explicit two-way data transfer) with otheraircraft or air traffic control systems about aircraft 3D position,speed, and/or identity. Position and speed are typically derived from aGNSS system, such as may provide absolute positioning. Over time, GNSSthreats may evolve and become more relevant in both commercial civil andmilitary airspaces.

It may be desirable to have a system that overcomes at least some ofthese limitations and which does not necessarily rely on GNSS positions.

SUMMARY

A system is disclosed in accordance with one or more illustrativeembodiments of the present disclosure. In one illustrative embodiment,the system may include a receiver or transmitter node. In anotherillustrative embodiment, the receiver or transmitter node may include acommunications interface with an antenna element and a controller. Inanother illustrative embodiment, the controller may include one or moreprocessors and have information of own node velocity and own nodeorientation relative to a common reference frame. In anotherillustrative embodiment, the receiver or transmitter node may be timesynchronized to apply Doppler corrections to signals, the Dopplercorrections associated with the receiver or transmitter node's ownmotions relative to the common reference frame, the Doppler correctionsapplied using Doppler null steering along Null directions. In anotherillustrative embodiment, the receiver node is configured to determine abearing angle based on the signals based on Doppler null steering; andto determine a range based on two-way time-of-flight based rangingsignals.

This Summary is provided solely as an introduction to subject matterthat is fully described in the Detailed Description and Drawings. TheSummary should not be considered to describe essential features nor beused to determine the scope of the Claims. Moreover, it is to beunderstood that both the foregoing Summary and the following DetailedDescription are example and explanatory only and are not necessarilyrestrictive of the subject matter claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. The use of the same reference numbers in different instances inthe description and the figures may indicate similar or identical items.Various embodiments or examples (“examples”) of the present disclosureare disclosed in the following detailed description and the accompanyingdrawings. The drawings are not necessarily to scale. In general,operations of disclosed processes may be performed in an arbitraryorder, unless otherwise provided in the claims.

FIG. 1 is a diagrammatic illustration of two nodes in a simplifiednetwork network and individual nodes thereof according to exampleembodiments of this disclosure.

FIG. 2A is a graphical representation of frequency shift profiles withinthe network of FIG. 1 .

FIG. 2B is a graphical representation of frequency shift profiles withinthe network of FIG. 1 .

FIG. 3 is a diagrammatic illustration of a transmitter node and areceiver node according to example embodiments of this disclosure.

FIG. 4A is a graphical representation of frequency shift profiles withinthe network of FIG. 3 .

FIG. 4B is a graphical representation of frequency shift profiles withinthe network of FIG. 3 .

FIG. 5 is a graph of sets for covering space.

FIG. 6 is a diagrammatic illustration of a transmitter node and areceiver node according to example embodiments of this disclosure.

FIG. 7 is a flow diagram illustrating a method according to exampleembodiments of this disclosure.

FIG. 8A is a diagrammatic illustration of nodes configured fordetermining bearing angle and range using two separate sets of antennaelements without necessarily using GNSS signals, according to exampleembodiments of this disclosure.

FIG. 8B is a diagrammatic illustration of nodes configured fordetermining the bearing angle and the range using a single set of atleast one antenna element without necessarily using GNSS signals,according to example embodiments of this disclosure.

DETAILED DESCRIPTION

Before explaining one or more embodiments of the disclosure in detail,it is to be understood that the embodiments are not limited in theirapplication to the details of construction and the arrangement of thecomponents or steps or methodologies set forth in the followingdescription or illustrated in the drawings. In the following detaileddescription of embodiments, numerous specific details may be set forthin order to provide a more thorough understanding of the disclosure.However, it will be apparent to one of ordinary skill in the art havingthe benefit of the instant disclosure that the embodiments disclosedherein may be practiced without some of these specific details. In otherinstances, well-known features may not be described in detail to avoidunnecessarily complicating the instant disclosure.

As used herein a letter following a reference numeral is intended toreference an embodiment of the feature or element that may be similar,but not necessarily identical, to a previously described element orfeature bearing the same reference numeral (e.g., 1, 1a, 1b). Suchshorthand notations are used for purposes of convenience only and shouldnot be construed to limit the disclosure in any way unless expresslystated to the contrary.

Further, unless expressly stated to the contrary, “or” refers to aninclusive or and not to an exclusive or. For example, a condition A or Bis satisfied by any one of the following: A is true (or present) and Bis false (or not present), A is false (or not present) and B is true (orpresent), and both A and B are true (or present).

In addition, use of “a” or “an” may be employed to describe elements andcomponents of embodiments disclosed herein. This is done merely forconvenience and “a” and “an” are intended to include “one” or “at leastone,” and the singular also includes the plural unless it is obviousthat it is meant otherwise.

Finally, as used herein any reference to “one embodiment”, “inembodiments” or “some embodiments” means that a particular element,feature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment disclosed herein. Theappearances of the phrase “in some embodiments” in various places in thespecification are not necessarily all referring to the same embodiment,and embodiments may include one or more of the features expresslydescribed or inherently present herein, or any combination orsub-combination of two or more such features, along with any otherfeatures which may not necessarily be expressly described or inherentlypresent in the instant disclosure.

Broadly speaking, embodiments herein are directed to systems and methodsfor achieving relative positioning between nodes using a combination ofdoppler nulling and time-of-flight based ranging (e.g., Two-Way Timingand Ranging System (TWTR), Two-Way Ranging, and the like).

In conventional IFF, TCAS, and TASC, determining positioning of nodes(e.g., aircraft) typically utilizes methods such as GNSS signals forabsolute positioning and data transfers for communicating positioningexplicitly (i.e., data packets used in various communication protocolssuch as those used in ADS-B and the like).

In some embodiments herein, on the other hand, it is contemplated thatusing doppler nulling signals for determining the bearing angle andtime-of-flight based ranging for determining the range may allow for avariety of benefits such as, but not necessarily limited to, higherefficiency (e.g., lower wattage signals for doppler nulling compared tothe signal-to-noise ratios required for relatively higher bandwidthexplicit data transfers), longer range, higher robustness againstspoofing/noise (e.g., higher robustness compared to GNSS), and/or thelike. In this regard, relative positioning via doppler nulling andranging may, among other limitations and benefits, replace absolutepositioning via GNSS in various airspace management methods and systems.

As described in U.S. patent application Ser. No. 18/130,285, filed Apr.3, 2023, which is herein incorporated by reference in its entirety,embodiments may utilize time synchronized scanning sequences (along withdirectionality) to improve metrics such as signal-to-noise ratio, signalacquisition time, speed of attaining situational awareness of attributesof surrounding nodes, range, and the like. In some embodiments, a zerovalue or near zero value (e.g., or the like such as a zero crossing) ofa calculated net frequency shift of a received signal is used todetermine a bearing angle between the source (e.g., Tx node) and thereceiving node using a time-of-arrival of the received signal. Thebearing angle may be made more accurate by combining (e.g., averaging)it with another bearing angle estimation determined from an angle ofpeak amplitude gain of the signal.

It is noted that U.S. patent application Ser. No. 17/857,920, filed Jul.5, 2022, is at least partially reproduced by at least some (or all) ofthe illustrations of FIGS. 1-7 and at least some (or all) of thecorresponding language for FIGS. 1-7 below. For example, at least someexamples of doppler nulling methods and systems may be betterunderstood, in a nonlimiting manner, by reference to FIGS. 1-7 . Suchembodiments and examples are provided for illustrative purposes and arenot to be construed as necessarily limiting. For instance, inembodiments the transmitter node may be stationary rather than movingand/or vice versa.

Moreover, and stated for purposes of navigating the disclosure only andnot to be construed as limiting, descriptions that may relate to otherlanguage not necessarily reproduced from U.S. patent application Ser.No. 17/857,920 include the discussion and figures after FIGS. 1-7 .

Referring now to FIGS. 1-7 , in some embodiments, a stationary receivermay determine a cooperative transmitter's direction and velocity vectorby using a Doppler null scanning approach in two dimensions. A benefitof the approach is the spatial awareness without exchanging explicitpositional information. Other benefits include discovery,synchronization, and Doppler corrections which are important forcommunications. Some embodiment may combine coordinated transmitterfrequency shifts along with the transmitter's motion induced Dopplerfrequency shift to produce unique net frequency shift signalcharacteristics resolvable using a stationary receiver to achievespatial awareness. Further, some embodiment may include athree-dimensional (3D) approach with the receiver and the transmitter inmotion.

Some embodiments may use analysis performed in a common reference frame(e.g., a common inertial reference frame, such as the Earth, which mayignore the curvature of Earth), and it is assumed that thecommunications system for each of the transmitter and receiver isinformed by the platform of its own velocity and orientation. Theapproach described herein can be used for discovery and tracking, butthe discussion here focuses on discovery which is often the mostchallenging aspect.

The meaning of the ‘Doppler Null’ can be explained in part through areview of the two-dimensional (2D) case without the receiver motion, andthen may be expounded on by a review of adding the receiver motion tothe 2D case, and then including receiver motion in the 3D case.

The Doppler frequency shift of a communications signal is proportionalto the radial velocity between transmitter and receiver, and anysignificant Doppler shift is typically a hindrance that should beconsidered by system designers. In contrast, some embodiments utilizethe Doppler effect to discriminate between directions with theresolution dictated by selected design parameters. Furthermore, suchembodiments use the profile of the net frequency shift as thepredetermined ‘Null’ direction scans through the angle space. Theresultant profile is sinusoidal with an amplitude that provides thetransmitter's speed, a zero net frequency shift when the ‘Null’direction aligns with the receiver, and a minimum indicating thedirection of the transmitter's velocity. It should be noted that thatthe transmitter cannot correct for Doppler in all directions at one timeso signal characteristics are different in each direction and aredifferent for different transmitter velocities as well. It is exactlythese characteristics that the receiver uses to determine spatialawareness. The received signal has temporal spatial characteristics thatcan be mapped to the transmitter's direction and velocity. This approachutilizes the concept of a ‘Null’ which is simply the direction where thetransmitter perfectly corrects for its own Doppler shift. The same‘Nulling’ protocol runs on each node and scans through all directions,such as via a scanning sequence of a protocol. Here we arbitrarilyillustrate the scanning with discrete successive steps of 10 degrees butin a real system; however, it should be understood that any suitablestep size of degrees may be used for Doppler null scanning.

As already mentioned, one of the contributions of some embodiments ispassive spatial awareness. Traditionally, spatial information forneighbor nodes (based on a global positioning system (GPS) and/or gyrosand accelerometers) can be learned via data communication.Unfortunately, spatial awareness via data communication, referred to asactive spatial awareness is possible only after communication hasalready been established, not while discovering those neighbor nodes.Data communication is only possible after the signals for neighbor nodeshave been discovered, synchronized and Doppler corrected. In contrast,in some embodiments, the passive spatial awareness described herein maybe performed using only synchronization bits associated withacquisition. This process can be viewed as physical layer overhead andtypically requires much lower bandwidth compared to explicit datatransfers. The physical layer overheads for discovery, synchronizationand Doppler correction have never been utilized for topology learningfor upper layers previously.

Traditionally, network topology is harvested via a series of data packetexchanges (e.g., hello messaging and link status advertisements). Thepassive spatial awareness may eliminate hello messaging completely andprovide a wider local topology which is beyond the coverage of hellomessaging. By utilizing passive spatial awareness, highly efficientmobile networking is possible. Embodiments may improve the functioningof a network, itself.

Referring to FIG. 1 , a multi-node communications network 100 isdisclosed. The multi-node communications network 100 may includemultiple communications nodes, e.g., a transmitter (Tx) node 102 and areceiver (Rx) node 104.

In embodiments, the multi-node communications network 100 may includeany multi-node communications network known in the art. For example, themulti-node communications network 100 may include a mobile network inwhich the Tx and Rx nodes 102, 104 (as well as every othercommunications node within the multi-node communications network) isable to move freely and independently. Similarly, the Tx and Rx nodes102, 104 may include any communications node known in the art which maybe communicatively coupled. In this regard, the Tx and Rx nodes 102, 104may include any communications node known in the art fortransmitting/transceiving data packets. For example, the Tx and Rx nodes102, 104 may include, but are not limited to, radios (such as on avehicle or on a person), mobile phones, smart phones, tablets, smartwatches, laptops, and the like. In embodiments, the Rx node 104 of themulti-node communications network 100 may each include, but are notlimited to, a respective controller 106 (e.g., control processor),memory 108, communication interface 110, and antenna elements 112. (Inembodiments, all attributes, capabilities, etc. of the Rx node 104described below may similarly apply to the Tx node 102, and to any othercommunication node of the multi-node communication network 100.)

In embodiments, the controller 106 provides processing functionality forat least the Rx node 104 and can include any number of processors,micro-controllers, circuitry, field programmable gate array (FPGA) orother processing systems, and resident or external memory for storingdata, executable code, and other information accessed or generated bythe Rx node 104. The controller 106 can execute one or more softwareprograms embodied in a non-transitory computer readable medium (e.g.,memory 108) that implement techniques described herein. The controller106 is not limited by the materials from which it is formed or theprocessing mechanisms employed therein and, as such, can be implementedvia semiconductor(s) and/or transistors (e.g., using electronicintegrated circuit (IC) components), and so forth.

In embodiments, the memory 108 can be an example of tangible,computer-readable storage medium that provides storage functionality tostore various data and/or program code associated with operation of theRx node 104 and/or controller 106, such as software programs and/or codesegments, or other data to instruct the controller 106, and possiblyother components of the Rx node 104, to perform the functionalitydescribed herein. Thus, the memory 108 can store data, such as a programof instructions for operating the Rx node 104, including its components(e.g., controller 106, communication interface 110, antenna elements112, etc.), and so forth. It should be noted that while a single memory108 is described, a wide variety of types and combinations of memory(e.g., tangible, non-transitory memory) can be employed. The memory 108can be integral with the controller 106, can comprise stand-alonememory, or can be a combination of both. Some examples of the memory 108can include removable and non-removable memory components, such asrandom-access memory (RAM), read-only memory (ROM), flash memory (e.g.,a secure digital (SD) memory card, a mini-SD memory card, and/or amicro-SD memory card), solid-state drive (SSD) memory, magnetic memory,optical memory, universal serial bus (USB) memory devices, hard diskmemory, external memory, and so forth.

In embodiments, the communication interface 110 can be operativelyconfigured to communicate with components of the Rx node 104. Forexample, the communication interface 110 can be configured to retrievedata from the controller 106 or other devices (e.g., the Tx node 102and/or other nodes), transmit data for storage in the memory 108,retrieve data from storage in the memory, and so forth. Thecommunication interface 110 can also be communicatively coupled with thecontroller 106 to facilitate data transfer between components of the Rxnode 104 and the controller 106. It should be noted that while thecommunication interface 110 is described as a component of the Rx node104, one or more components of the communication interface 110 can beimplemented as external components communicatively coupled to the Rxnode 104 via a wired and/or wireless connection. The Rx node 104 canalso include and/or connect to one or more input/output (I/O) devices.In embodiments, the communication interface 110 includes or is coupledto a transmitter, receiver, transceiver, physical connection interface,or any combination thereof.

It is contemplated herein that the communication interface 110 of the Rxnode 104 may be configured to communicatively couple to additionalcommunication interfaces 110 of additional communications nodes (e.g.,the Tx node 102) of the multi-node communications network 100 using anywireless communication techniques known in the art including, but notlimited to, GSM, GPRS, CDMA, EV-DO, EDGE, WiMAX, 3G, 4G, 4G LTE, 5G,WiFi protocols, RF, LoRa, and the like.

In embodiments, the antenna elements 112 may include directional oromnidirectional antenna elements capable of being steered or otherwisedirected (e.g., via the communications interface 110) for spatialscanning in a full 360-degree arc (114) relative to the Rx node 104 (oreven less than a full 360 degree arc).

In embodiments, the Tx node 102 and Rx node 104 may one or both bemoving in an arbitrary direction at an arbitrary speed, and maysimilarly be moving relative to each other. For example, the Tx node 102may be moving relative to the Rx node 104 according to a velocity vector116, at a relative velocity V_(TX) and a relative angular direction (anangle α relative to an arbitrary direction 118 (e.g., due east); θ maybe the angular direction of the Rx node relative to due east.

In embodiments, the Tx node 102 may implement a Doppler nullingprotocol. For example, the Tx node 102 may adjust its transmit frequencyto counter the Doppler frequency offset such that there is no netfrequency offset (e.g., “Doppler null”) in a Doppler nulling direction120 (e.g., at an angle ϕ relative to the arbitrary direction 118). Thetransmitting waveform (e.g., the communications interface 110 of the Txnode 102) may be informed by the platform (e.g., the controller 106) ofits velocity vector and orientation (e.g., a, V_(T)) and may adjust itstransmitting frequency to remove the Doppler frequency shift at eachDoppler nulling direction 120 and angle ϕ.

To illustrate aspects of some embodiments, we show the 2D dependence ofthe net frequency shift for a stationary receiver as a function of Nulldirection across the horizon, as shown in a top-down view of FIG. 1 ,where the receiver node 104 is stationary and positioned θ from eastrelative to the transmitter, the transmitter node 102 is moving with aspeed

and direction a from east and a snapshot of the scanning ϕ which is the‘Null’ direction, exemplarily shown as 100 degrees in this picture.

The Doppler shift is a physical phenomenon due to motion and can beconsidered as a channel effect. In this example the transmitter node 102is the only moving object, so it is the only source of Doppler shift.The Doppler frequency shift as seen by the receiver node 104 due to thetransmitter node 102 motion is:

${\frac{\Delta f_{DOPPLER}}{f} = {\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}{\cos\left( {\theta - \alpha} \right)}}},$

where c is the speed of light

The other factor is the transmitter frequency adjustment term thatshould exactly compensate the Doppler shift when the ‘Null’ directionaligns with the receiver direction. It is the job of the transmitternode 102 to adjust its transmit frequency according to its own speed(|{right arrow over (V_(T))}|), and velocity direction (α). Thattransmitter frequency adjustment (Δf_(T)) is proportional to thevelocity projection onto the ‘Null’ direction (

) and is:

$\frac{\Delta f_{T}}{f} = {{- \frac{❘\overset{\rightarrow}{V_{T}}❘}{c}}{\cos\left( {\varphi - \alpha} \right)}}$

The net frequency shift seen by the receiver is the sum of the twoterms:

$\frac{\Delta f_{net}}{f} = {\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}\left\lbrack {{\cos\left( {\theta - \alpha} \right)} - {\cos\left( {\varphi - \alpha} \right)}} \right\rbrack}$

It is assumed that the velocity vector and the direction changes slowlycompared to the periodic measurement of Δf_(net). Under thoseconditions, the unknown parameters (from the perspective of the receivernode 104) of α, |{right arrow over (V_(T))}|, and θ are constants.

Furthermore, it is assumed that the receiver node 104 has animplementation that resolves the frequency of the incoming signal, aswould be understood to one of ordinary skill in the art.

FIG. 2A shows the resulting net frequency shift as a function of the‘Null’ direction for scenarios where a stationary receiver is East ofthe transmitter (theta=0), and with a transmitter speed of 1500 metersper second (m/s). FIG. 2B shows the results for a stationary receiverand for several directions with an Eastern transmitter node velocitydirection (alpha=0). The frequency shifts are in units of parts permillion (ppm). As shown in FIGS. 2A and 2B, the amplitude is consistentwith the transmitter node's 102 speed of 5 ppm [|{right arrow over(V_(T))}|/c*(1×10⁶)] regardless of the velocity direction or position,the net frequency shift is zero when the ‘Null’ angle is in the receiverdirection (when ϕ=θ), and the minimum occurs when the ‘Null’ is alignedwith the transmitter node's 102 velocity direction (when ϕ=α).

From the profile, the receiver node 104 can therefore determine thetransmitter node's 102 speed, the transmitter node's 102 heading, andthe direction of the transmitter node 102 is known to at most, one oftwo locations (since some profiles have two zero crossings). It shouldbe noted that the two curves cross the y axis twice (0 & 180 degrees inFIG. 2A, and ±90 degrees in FIG. 2B) so there is initially an instanceof ambiguity in position direction. In this case the receiver node 104knows the transmitter node 102 is either East or West of the receivernode 104.

Referring to FIG. 3 , a multi-node communications network 100 isdisclosed. The multi-node communications network 100 may includemultiple communications nodes, e.g., a transmitter (Tx) node 102 and areceiver (Rx) node 104. As shown in FIG. 3 both of the transmitter node102 and the receiver node 104 are in motion in two dimensions.

The simultaneous movement scenario is depicted in FIG. 3 where thereceiver node 104 is also moving in a generic velocity characterized bya speed

and the direction, β. The protocol for the moving receiver node 104incorporates a frequency adjustment on the receiver node's 104 side tocompensate for the receiver node's 104 motion as well. The equationshave two additional terms. One is a Doppler term for the motion of thereceiver and the second is frequency compensation by the receiver.

Again, the Doppler shift is a physical phenomenon due to motion and canbe considered as a channel effect, but in this case both the transmitternode 102 and the receiver node 104 are moving so there are two Dopplershift terms. The true Doppler shift as seen by the receiver due to therelative radial velocity is:

$\frac{\Delta f_{DOPPLER}}{f} = {{\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}{\cos\left( {\theta - \alpha} \right)}} - {\frac{❘\overset{\rightarrow}{V_{R}}❘}{c}{\cos\left( {\theta - \beta} \right)}}}$

The other factors are the transmitter node 102 and receiver node 104frequency adjustment terms that exactly compensates the Doppler shiftwhen the ‘Null’ direction aligns with the receiver direction. It is thejob of the transmitter node 102 to adjust the transmitter node's 102transmit frequency according to its own speed (|{right arrow over(V_(T))}|), and velocity direction (α). That transmitter node frequencyadjustment is proportional to the velocity projection onto the ‘Null’direction (

) and is the first term in the equation below.

It is the job of the receiver node 104 to adjust the receiver nodefrequency according to the receiver node's 104 own speed (|{right arrowover (V_(R))}|), and velocity direction (β). That receiver nodefrequency adjustment is proportional to the velocity projection onto the‘Null’ direction (

) and is the second term in the equation below. The receiver nodefrequency adjustment can be done to the receive signal prior to thefrequency resolving algorithm or could be done within the algorithm.

$\frac{\Delta f_{{T\&}R}}{f} = {{{- \frac{❘\overset{\rightarrow}{V_{T}}❘}{c}}{\cos\left( {\varphi - \alpha} \right)}} + {\frac{❘\overset{\rightarrow}{V_{R}}❘}{c}{\cos\left( {\varphi - \beta} \right)}}}$

The net frequency shift seen by the receiver is the sum of all terms:

$\frac{\Delta f_{net}}{f} = {{\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}\left\lbrack {{\cos\left( {\theta - \alpha} \right)} - {\cos\left( {\varphi - \alpha} \right)}} \right\rbrack} - {\frac{❘\overset{\rightarrow}{V_{R}}❘}{c}\left\lbrack {{\cos\left( {\theta - \beta} \right)} - {\cos\left( {\varphi - \beta} \right)}} \right\rbrack}}$

Again, it is assumed that the receiver node 104 has an implementationthat resolves the frequency of the incoming signal, as would beunderstood in the art.

Also, it is assumed that the velocity vector and direction changesslowly compared to the periodic measurement of Δf_(net). Again, undersuch conditions, the unknown parameters (from the perspective of thereceiver node 104) α, |{right arrow over (V_(T))}|, and θ are constants.When the velocity vector or direction change faster, then this changecould be tracked, for example if the change is due to slow changes inacceleration.

The net frequency shift for the two-dimensional (2D) moving receivernode 104 approach is shown in FIGS. 4A and 4B for several scenario casesof receiver node location, θ, and transmitter node and receiver nodespeeds (|{right arrow over (V_(T))}| & |{right arrow over (V_(R))}|), aswell as transmitter node and receiver node velocity direction (α and β).FIG. 4A has different speeds for the transmitter node 102 and receivernode 104 as well as the receiver node location of θ=0. FIG. 4B has thesame speed for the transmitter node and receiver node. Similarly, thereare three concepts to notice here:

-   -   The amplitude is consistent with the relative velocity between        transmitter node 102 and receiver node 104 [|(|{right arrow over        (V_(T))}|cos (α)−|{right arrow over (V_(R))}|cos (β))|/c*1e6)].    -   The net frequency shift is zero when the ‘Null’ angle is in the        receiver direction (when ϕ=θ).    -   The minimum occurs when the ‘Null’ is aligned with the relative        velocity direction (when ϕ=angle(|{right arrow over (V_(T))}|cos        (α)−|{right arrow over (V_(R))}|cos (β))).

Again, there is an initial dual point ambiguity with the position, θ,but the transmitter node's 102 speed and velocity vector is known.

Referring now to FIG. 5 , while the 2D picture is easier to visualize,the same principles apply to the 3D case. FIG. 5 shows a number ofdirection sets needed to span 3D and 2D space with different cone sizes(cone sizes are full width). Before diving into the equations, it'sworth commenting on the size of the space when including anotherdimension. For example, when a ‘Null’ step size of 10 degrees was usedin the previous examples, it took 36 sets to span the 360 degrees in 2D.Thus, if an exemplary detection angle of 10 degrees is used (e.g., adirectional antenna with 10-degree cone) it would take 36 sets to coverthe 2D space. The 3D fractional coverage can be computed by calculatingthe coverage of a cone compared to the full 4 pi steradians. Thefraction is equal to the integral

${{FractionCoverage}3D} = {\frac{\int_{0}^{ConeSiz{e/2}}{r^{2}{\sin\left( \theta^{\prime} \right)}d\theta^{\prime}d\varphi}}{4\pi r^{2}} = \frac{1 - {\cos\left( {{ConeSize}/2} \right)}}{2}}$FractionCoverage2D = 2π/ConeSize

The number of sets to span the space is shown in FIG. 5 for both the 2Dand 3D cases which correlates with discovery time. Except for narrowcone sizes, the number of sets is not drastically greater for the 3Dcase (e.g., approximately 15 times at 10 degrees, 7 time at 20 degrees,and around 5 times at 30 degrees). Unless systems are limited to verynarrow cone sizes, the discovery time for 3D searches is notoverwhelming compared to a 2D search.

Referring now to FIG. 6 , a multi-node communications network 100 isdisclosed. The multi-node communications network 100 may includemultiple communications nodes, e.g., a transmitter (Tx) node 102 and areceiver (Rx) node 104. As shown in FIG. 6 both of the transmitter node102 and the receiver node 104 are in motion in three dimensions.

The 3D approach to Doppler nulling follows the 2D approach but it isillustrated here with angles and computed vectorially for simplicity.

In three dimensions, it is convenient to express the equations in vectorform which is valid for 2 or 3 dimensions. FIG. 6 shows the geometry in3 dimensions where

is the unit vector pointing to the receiver from the transmitter, and

is the unit vector pointing in the ‘Null’ direction defined by theprotocol.

The true Doppler shift as seen by the receiver node 104 due to therelative radial velocity which is the projection onto the

vector:

$\frac{\Delta f_{DOPPLER}}{f} = {{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}$

The nulling protocol adjusts the transmit node frequency and receivernode frequency due to their velocity projections onto the

direction

$\frac{\Delta f_{T}}{f} = {{{- \frac{1}{c}}{\overset{\rightarrow}{V_{T}} \cdot}} + {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}$

The net frequency shift seen by the receiver node 104 is the sum of allterms:

$\frac{\Delta f_{net}}{f} = {{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} + {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}$

The net frequency shift for the 3D moving receiver node 104 approach isnot easy to show pictorially but can be inspected with mathematicalequations to arrive at useful conclusions. The first two terms are theDoppler correction (DC) offset and the last two terms are the nulldependent terms. Since the

is the independent variable, the maximum occurs when({right arrow over(V_(R))}−{right arrow over (V_(T))}) and

are parallel and is a minimum when they are antiparallel. Furthermore,the relative speed is determined by the amplitude,

${Amplitude} = {\frac{1}{c}{❘{\overset{\rightarrow}{V_{R}} - \overset{\rightarrow}{V_{T}}}❘}}$

Lastly, the net frequency is zero when the

is parallel (i.e., parallel in same direction, as opposed toanti-parallel) to

${\frac{\Delta f_{net}}{f} = {0{when}}},{{{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}} = {{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}}$

or, ({right arrow over (V_(T))}−{right arrow over (V_(R))})·

=({right arrow over (V_(T))}−{right arrow over (V_(R))})·

For the 3D case:

-   -   The amplitude is consistent with the relative velocity between        transmitter node 102 and receiver node 104 [|{right arrow over        (V_(R))}−{right arrow over (V_(T))}|/c].    -   The net frequency shift is zero when the ‘Null’ angle is in the        receiver node direction, ({right arrow over (V_(T))}−{right        arrow over (V_(R))})·        =({right arrow over (V_(T))}−{right arrow over (V_(R))})·    -   The minimum occurs when the ‘Null’ is aligned with the relative        velocity direction.

Referring still to FIG. 6 , in some embodiments, the system (e.g., themulti-node communications network 100) may include a transmitter node102 and a receiver node 104. Each node of the transmitter node 102 andthe receiver node 104 may include a communications interface 110including at least one antenna element 112 and a controller operativelycoupled to the communications interface, the controller 106 includingone or more processors, wherein the controller 106 has information ofown node velocity and own node orientation. The transmitter node 102 andthe receiver node 104 may be in motion (e.g., in two dimensions or inthree dimensions). The transmitter node 102 and the receiver node 104may be time synchronized to apply Doppler corrections associated withsaid node's own motions relative to a common reference frame (e.g., acommon inertial reference frame (e.g., a common inertial reference framein motion or a stationary common inertial reference frame)). The commonreference frame may be known to the transmitter node 102 and thereceiver node 104 prior to the transmitter node 102 transmitting signalsto the receiver node 104 and prior to the receiver node 104 receivingthe signals from the transmitter node 102. In some embodiments, thesystem is a mobile network comprising the transmitter node 102 and thereceiver node 104.

In some embodiments, the applying of the Doppler corrections associatedwith the receiver node's own motions relative to the common referenceframe is based on a common reference frequency. For example, a commonreference frequency may be adjusted by a node's own motions to cancelout those motions in reference to the null angle. This common referencefrequency may be known by each node prior to transmission and/orreception of the signals. In some embodiments, calculating the netfrequency change seen by the receiver node 104 is based on the commonreference frequency. For example, the net frequency change may be adifference between a measured frequency of the signals and the commonreference frequency.

For purposes of discussing the receiver node 104, a “source” generallyrefers to a source of a received signal, multiple sources of multiplesignals, a single source of multiple signals, and/or the like. Forexample, a source may be a transmitter node 102 configured to applyDoppler corrections as disclosed herein and in applications from whichpriority is claimed and/or incorporated by reference. In this regard, areceiver node 104 may determine one or more attributes of the source(e.g., bearing between the receiver node 104 and the source, bearing ofthe velocity of the source, amplitude/speed of the velocity, range, andthe like). In some embodiments, the receiver node 104 and the source(e.g., transmitter node 102) are configured to use a same, compatible,and/or similar Doppler correction, protocol, common reference frame,common reference frequency, time synchronization, and/or the like suchthat the receiver node 104 may determine various attributes of thesource. Note, in some embodiments, that one or more of these may beknown ahead of time, be determined thereafter, included as fixedvariable values as part of the protocol, and/or determined dynamically(in real time) as part of the protocol. For example, the protocol maydetermine that certain common reference frames should be used in certainenvironments, such as using GPS coordinates on land and a naval shipbeacon transmitter common reference frame location (which may be mobile)over certain areas of ocean, which may dynamically change in real timeas a location of a node changes.

In some embodiments, the transmitter node 102 and the receiver node 104are time synchronized via synchronization bits associated withacquisition. For example, the synchronization bits may operate asphysical layer overhead.

In some embodiments, the transmitter node 102 is configured to adjust atransmit frequency according to an own speed and an own velocitydirection of the transmitter node 102 so as to perform atransmitter-side Doppler correction. In some embodiments, the receivernode 104 is configured to adjust a receiver frequency of the receivernode 104 according to an own speed and an own velocity direction of thereceiver node 104 so as to perform a receiver-side Doppler correction.In some embodiments, an amount of adjustment of the adjusted transmitfrequency is proportional to a transmitter node 102 velocity projectiononto a Doppler null direction, wherein an amount of adjustment of theadjusted receiver frequency is proportional to a receiver node 104velocity projection onto the Doppler null direction. In someembodiments, the receiver node 102 is configured to determine a relativespeed between the transmitter node 102 and the receiver node 104. Insome embodiments, the receiver node 104 is configured to determine adirection that the transmitter node 102 is in motion and a velocityvector of the transmitter node 102. In some embodiments, a maximum netfrequency shift for a Doppler correction by the receiver node 104 occurswhen a resultant vector is parallel to the Doppler null direction,wherein the resultant vector is equal to a velocity vector of thereceiver node 104 minus the velocity vector of the transmitter node 102.In some embodiments, a minimum net frequency shift for a Dopplercorrection by the receiver node 104 occurs when a resultant vector isantiparallel to the Doppler null direction, wherein the resultant vectoris equal to a velocity vector of the receiver node 104 minus thevelocity vector of the transmitter node 102. In some embodiments, a netfrequency shift for a Doppler correction by the receiver node 104 iszero when a vector pointing to the receiver node from the transmitternode 102 is parallel to the Doppler null direction.

Referring now to FIG. 7 , an exemplary embodiment of a method 700according to the inventive concepts disclosed herein may include one ormore of the following steps. Additionally, for example, some embodimentsmay include performing one or more instances of the method 700iteratively, concurrently, and/or sequentially. Additionally, forexample, at least some of the steps of the method 700 may be performedin parallel and/or concurrently. Additionally, in some embodiments, atleast some of the steps of the method 700 may be performednon-sequentially.

A step 702 may include providing a transmitter node and a receiver node,wherein each node of the transmitter node and the receiver node are timesynchronized, wherein each node of the transmitter node and the receivernode are in motion, wherein each node of the transmitter node and thereceiver node comprises a communications interface including at leastone antenna element, wherein each node of the transmitter node and thereceiver node further comprises a controller operatively coupled to thecommunications interface, the controller including one or moreprocessors, wherein the controller has information of own node velocityand own node orientation.

A step 704 may include based at least on the time synchronization,applying, by the transmitter node, Doppler corrections to thetransmitter node's own motions relative to a common reference frame.

A step 706 may include based at least on the time synchronization,applying, by the receiver node, Doppler corrections to the receivernode's own motions relative to the common reference frame, wherein thecommon reference frame is known to the transmitter node and the receivernode prior to the transmitter node transmitting signals to the receivernode and prior to the receiver node receiving the signals from thetransmitter node.

Further, the method 700 may include any of the operations disclosedthroughout.

The null scanning/steering technique discussed herein illustrates asystem and a method for spatial awareness from resolving the temporalspatial characteristics of the transmitter node's 102 radiation. Thisapproach informs the receiver node 104 of the relative speed between thetransmitter node 102 and receiver node 104 as well as the transmitternode direction and transmitter node velocity vector. This approachincludes scanning through all directions and has a high sensitivity(e.g., low net frequency shift) when the null direction is aligned withthe transmitter node direction. This approach can be implemented on ahighly sensitive acquisition frame which is typically much moresensitive than explicit data transfers which allow for theultra-sensitive spatial awareness with relatively low power.

This sentence may mark an end to the (at least partially) reproducedlanguage from U.S. patent application Ser. No. 17/857,920 correspondingto the (at least partially) reproduced FIGS. 1-7 . However, note thatthis paragraph is nonlimiting, and changes may have been made andlanguage added or removed, and not all the language above orcorresponding figures above are necessarily reproduced from U.S. patentapplication Ser. No. 17/857,920.

Embodiments of the present disclosure may extend doppler nulling, incombination with a ranging technique, for use in airspace management.For example, rather than relying on GNSS for absolute positioning forairspace management, a ranging technique may be combined with dopplernulling to achieve relative positioning.

Embodiments may be used in many commercial and civilian applicationssuch as, but not necessarily limited to, airspace management such asnode identification (e.g., identifying airplane or drone nodes near alanding area), terminal airspace management (e.g., giving guidance tonodes based on their proximity to each other), and/or traffic avoidancedeterminations (e.g., determining risks of collisions and alerting ordirecting a node to avoid the risk of collision). Applications may alsoinclude military applications such as Identification Friend or Foe(IFF), military base airspace management, and/or the like.

The deep-noise addition to Doppler-nulling (e.g., U.S. patentapplication Ser. No. 17/534,061) may offer a viable mechanism forterminals to synchronize across long distances using very low power,thus minimizing potential for transmitter observation by anout-of-network receiver or interference to an out-of-network receiver.

Examples of doppler nulling methods include, but are not limited to,methods and other descriptions (e.g., at least some theory andmathematical basis) are disclosed in U.S. patent application Ser. No.17/233,107, filed Apr. 16, 2021, which is hereby incorporated byreference in its entirety; U.S. patent application Ser. No. 17/534,061,filed Nov. 23, 2021, which is hereby incorporated by reference in itsentirety; and U.S. patent application Ser. No. 17/857,920, filed Jul. 5,2022, which is hereby incorporated by reference in its entirety. Inembodiments, doppler nulling methods allow for benefits such as, but notlimited to, relatively quickly and/or efficiently detecting transmitternodes and determining transmitter node attributes (e.g., transmitternode speed, transmitter node bearing, relative bearing of transmitternode relative to receiver node, relative distance of transmitter noderelative to receiver node, and the like).

FIG. 8A is a diagrammatic illustration of a system 100 with nodes 102,104 configured for determining relative positions (e.g., bearing angle808 and range 806) using two separate sets of antenna elements 112 a,112 b without necessarily using GNSS signals, according to exampleembodiments of this disclosure.

In some embodiments, while FIG. 8A shows two separate antennasub-systems (each with their own set of antenna elements 112 a, 112 b),please note that FIGS. 8A and 8B are nonlimiting and any of the nodes102, 104 may include any number of sets of at least one antenna element112 to perform what is described in the present disclosure. For example,one node may use a single antenna element as shown in FIG. 8B, whileanother node may use multiple sets of antenna elements 112 a, 112 b asshown in FIG. 8A. Also note that the transmitter node 102 and receivernode 104 herein generally may individually, or both, be capable oftransmitting and receiving, and are not necessarily limited totransmitting or receiving. For example, for an IFF embodiment, thereceiver node 104 may be configured to receive doppler signals 804 andto also transmit its own doppler signals 804, ranging signals 802,and/or interrogating signals using one or more antenna elements (e.g.,112 a, 112 b, 112, and/or the like).

In embodiments, the system 100 determines bearing angle 808 and range806 using different techniques. For example, bearing angle 808 may bedetermined using doppler nulling and range 806 may be determined usingtwo-way time-of-flight based ranging.

Generally, two-way time-of-flight based ranging includes making a rangedetermination of a received signal 802 based on the time-of-flight ofthe signal 802. Ranging may involve some sort of two-way cooperationand/or synchronization between nodes 102, 104. For example, two-waytime-of-flight based ranging may include nodes configured to send andreceive signals such that the time-of-flight of the signal 802 is adetermining factor in the calculated range 806. An approximation of thespeed (c) (e.g., speed of light in air) of the signal 802 is also used.For example, the first node 104 may be configured to send a firstranging signal 802 at a time (t1) which is received by a second node 102at another time (t2). The second node 102 may be configured to send backa signal 802 at t3 in response, based on a known delay (t3−t2) it takesto receive and then send such a response. The first node 104 receivesthis response 802 at t4. In this two-way time-of-flight based rangingtechnique, the range 806 may be determined by a formula such as thefollowing: range=c*((t4−t1)−(t3−t2))/2. The division by 2 accounts forthe fact that the signal 802 travels the distance twice—once from thefirst node 104 to the second node 102 and once from the second node 102back to the first node 104. Note that this example is nonlimiting, andany number of two-way time-of-flight based ranging techniques may beused, such as, but not necessarily limited to, establishing a timesynchronization between nodes 102, 104 and determining the range 806based on the arrival time of a single signal 802 and an expected time ofwhen the single signal 802 was sent based on a known shared protocol andthe time synchronization. In this example, the range=c*(t2−t1), where t1is the expected time of when the single signal 802 was sent and t2 isthe arrival time.

FIG. 8B is a diagrammatic illustration of nodes configured fordetermining the bearing angle 808 and the range 806 using a single setof at least one antenna element 112 without necessarily using GNSSsignals, according to example embodiments of this disclosure. Comparedto FIG. 8A, FIG. 8B uses a single set of antenna elements 112.

For example, the signals 804 (i.e., doppler signals associated with anull direction 120 of FIG. 1 ) used for determining bearing angle 808may be sent and/or received by a single set of antenna elements (e.g.,at least one first antenna element 112 of the receiver node 104 and/ortransmitter node 102). In addition, the ranging signal 802 may be sentand/or received by the (same) set of antenna elements (e.g., the atleast one second antenna element 112 of the receiver node 104 and/ortransmitter node 102). In this regard, the same antenna elements 112 maybe used for both doppler nulling signals 804 and ranging signals 802.Further, the doppler nulling signals 804 and ranging signals 802 may bedifferent signals sent at different times and/or the same signal sent atthe same time.

Referring now to FIGS. 8A and/or 8B generally, various embodiments aredescribed.

In some embodiments, at least the receiver node 104 is configured toperform an airspace management operation based on the relative position.For example, the transmitter node(s) 102 may be aircraft configured toobey airspace management directives, but not necessarily configured tomake all airspace management determinations. For example, the receivernode 104 may be a ground station (e.g., air traffic control system),central management node (e.g., aircraft carrier), central server, cloudserver, and/or the like configured to manage airspace. Note that, insome embodiments, the transmitting node 102 is also configured toperform airspace management operations.

In some embodiments, managing airspace may include operations, steps,and the like related to, but not necessarily limited to, executing anidentification protocol configured to differentiate between friendly andadversarial nodes, performing a traffic collision avoidancedetermination configured to avoid a collision of a node, and/orproviding terminal airspace guidance to one or more nodes.

In some embodiments, Doppler null steering may be used to replaceexisting IFF, TCAS, and TASC systems. In other embodiments, Doppler nullsteering may be used to augment/enhance existing systems by addingDoppler null scanning as an overlay to the existing systems. In someexamples, existing systems with added Doppler null steering may beconfigured to also (alternatively) work properly without the Dopplernull steering, although with degraded performance. This may allowexisting systems to transition to using Doppler null steering. In someembodiments, new systems (e.g., commercial and/or military systems) maybe configured to use Doppler null steering without needing legacypositioning for operations such as IFF, TCAS, and TASC.

For example, executing an identification protocol may include receivingsignals 804 (e.g., being configured to listen for doppler nullingsignals 804) and, once received, determining relative positioning, andtransmitting an interrogation signal (not shown) configured to query thetransmitter node 102. For instance, embodiments herein may be compatiblewith existing and/or modified IFF protocols. In this way, rather than(or in combination with) using conventional IFF techniques such asscanning surveillance radar to search for and identify nodes 102 forinterrogation purposes, IFF protocols may be configured to be compatiblewith embodiments herein that use doppler nulling. IFF systems usingdoppler nulling may more quickly identify relative positions of nodes104 so that interrogation signals may be sent out quickly.

By way of another example, performing a traffic collision avoidancedetermination configured to avoid a collision of a node (e.g., any nodesuch as other transmitting nodes 104) may include performing TCASoperations, such as using existing TCAS protocols modified for dopplernulling. For instance, the system 100 may be configured for TCASoperations.

By way of another example, providing terminal airspace guidance to oneor more nodes (e.g., any node such as the transmitter node 104) mayinclude performing TASC operations, such as using existing TASCprotocols modified for doppler nulling. For instance, the system 100 maybe configured for TASC operations. For example, the receiver node 104may issue a Traffic Advisory (TA) to the transmitter node 102 based onthe relative position of the transmitter node 102 relative to closeproximity to other aircraft nodes in the area based on the relativepositions of the nodes.

Note that embodiments herein do not necessarily require addingadditional equipment to existing systems. For example, a software updatemay allow some currently certified equipment to perform doppler nullingin combination with ranging and still be compliant with IFF, TCAS,and/or TASC message protocols. The system 100 may be configured (e.g.,via program instructions stored on memory 108) to determine IFF, TCAS,and/or TASC messages based on relative positions determined usingembodiments of the present disclosure and route the messages over anappropriate interface (e.g., MIL-STD 1553 and/or ethernet) to anavigation and/or flight system of the system 100.

For at least purposes of this disclosure, ‘Doppler nulling’ means‘Doppler null steering’, ‘Doppler null scanning’, and the like.

It is to be understood that embodiments of the methods disclosed hereinmay include one or more of the steps described herein. Further, suchsteps may be carried out in any desired order and two or more of thesteps may be carried out simultaneously with one another. Two or more ofthe steps disclosed herein may be combined in a single step, and in someembodiments, one or more of the steps may be carried out as two or moresub-steps. Further, other steps or sub-steps may be carried in additionto, or as substitutes to one or more of the steps disclosed herein.

Although inventive concepts have been described with reference to theembodiments illustrated in the attached drawing figures, equivalents maybe employed and substitutions made herein without departing from thescope of the claims. Components illustrated and described herein aremerely examples of a system/device and components that may be used toimplement embodiments of the inventive concepts and may be replaced withother devices and components without departing from the scope of theclaims. Furthermore, any dimensions, degrees, and/or numerical rangesprovided herein are to be understood as non-limiting examples unlessotherwise specified in the claims.

We claim:
 1. A system comprising: a transmitter node and a receivernode, wherein each node of the transmitter node and the receiver nodecomprises: a communications interface comprising at least one antennaelement; and a controller operatively coupled to the communicationsinterface, the controller including one or more processors, wherein thecontroller has information of own node velocity and own nodeorientation; wherein each node of the transmitter node and the receivernode are in motion relative to each other, wherein each node of thetransmitter node and the receiver node are time synchronized to applyDoppler corrections associated with said node's own motions relative toa common reference frame, wherein the transmitter node is configured toapply the Doppler corrections to signals using Doppler null steeringalong a plurality of Null directions based on the transmitter node's ownmotions, wherein the common reference frame is known to the transmitternode and the receiver node prior to the transmitter node transmittingthe signals to the receiver node and prior to the receiver nodereceiving the signals from the transmitter node, wherein the receivernode is configured to determine a relative position between the receivernode and the transmitter node, the relative position comprising abearing angle and a range, wherein determining the relative positioncomprises: determining the bearing angle between the receiver node andthe transmitter node based on the signals based on the Doppler nullsteering; and determining the range between the receiver node and thetransmitter node based on a two-way time-of-flight based ranging betweenthe receiver node and the transmitter node.
 2. The system of claim 1,wherein at least the receiver node is configured to perform an airspacemanagement operation based on the relative position.
 3. The system ofclaim 2, wherein the airspace management operation comprises: anexecution of an identification protocol configured to differentiatebetween friendly and adversarial nodes.
 4. The system of claim 3,wherein the execution of the identification protocol comprises thereceiver node being configured to transmit an interrogation signalconfigured to query the transmitter node.
 5. The system of claim 2,wherein the airspace management operation comprises: a traffic collisionavoidance determination configured to avoid a collision of a node. 6.The system of claim 2, wherein the airspace management operationcomprises: providing terminal airspace guidance to one or more nodes. 7.The system of claim 2, wherein the relative positioning is used toestablish spatial awareness of a plurality of nodes.
 8. The system ofclaim 1, wherein the bearing angle is a three dimensional bearing angle.9. A system comprising: a receiver node comprising: a communicationsinterface comprising at least one antenna element; and a controlleroperatively coupled to the communications interface, the controllerincluding one or more processors, wherein the controller has informationof own node velocity and own node orientation relative to a commonreference frame; wherein the receiver node is time synchronized to applyDoppler corrections associated with the receiver node's own motionsrelative to the common reference frame, wherein the common referenceframe is known to the receiver node prior to the receiver node receivingsignals from a transmitter node, wherein the receiver node is configuredto process the signals according to the Doppler corrections to thesignals applied using Doppler null steering along a plurality of Nulldirections based on the transmitter node's own motions, wherein thereceiver node is configured to determine a relative position between thereceiver node and the transmitter node, the relative position comprisinga bearing angle and a range, wherein determining the relative positioncomprises: determining the bearing angle between the receiver node andthe transmitter node based on the signals based on the Doppler nullsteering; and determining the range between the receiver node and thetransmitter node based on a two-way time-of-flight based ranging betweenthe receiver node and the transmitter node.
 10. The system of claim 9,wherein the receiver node is configured to perform an airspacemanagement operation based on the relative position.
 11. The system ofclaim 10, wherein the airspace management operation comprises: anexecution of an identification protocol configured to differentiatebetween friendly and adversarial nodes.
 12. The system of claim 10,wherein the airspace management operation comprises: a traffic collisionavoidance determination configured to avoid a collision of a node. 13.The system of claim 10, wherein the airspace management operationcomprises: providing terminal airspace guidance to one or more nodes.14. A system comprising: a transmitter node comprising: a communicationsinterface comprising at least one antenna element; and a controlleroperatively coupled to the communications interface, the controllerincluding one or more processors, wherein the controller has informationof own node velocity and own node orientation relative to a commonreference frame; wherein the transmitter node is time synchronized toapply Doppler corrections associated with the transmitter node's ownmotions relative to the common reference frame, wherein the transmitternode is configured to apply the Doppler corrections to signals usingDoppler null steering along a plurality of Null directions based on thetransmitter node's own motions, wherein the common reference frame isknown to the transmitter node prior to the transmitter node transmittingthe signals, wherein the transmitter node is configured to determine arelative position between the transmitter node and a receiver node, therelative position comprising a bearing angle and a range, whereindetermining the relative position comprises: determining the bearingangle between the receiver node and the transmitter node based on thesignals based on the Doppler null steering; and determining the rangebetween the receiver node and the transmitter node based on a two-waytime-of-flight based ranging between the receiver node and thetransmitter node.
 15. The system of claim 14, wherein the receiver nodeis configured to perform an airspace management operation based on therelative position.
 16. The system of claim 15, wherein the airspacemanagement operation comprises: an execution of an identificationprotocol configured to differentiate between friendly and adversarialnodes.
 17. The system of claim 15, wherein the airspace managementoperation comprises: a traffic collision avoidance determinationconfigured to avoid a collision of a node.
 18. The system of claim 15,wherein the airspace management operation comprises: providing terminalairspace guidance to one or more nodes.
 19. The system of claim 14,wherein the bearing angle is a two dimensional bearing angle.
 20. Thesystem of claim 19, wherein the bearing angle is a three dimensionalbearing angle.